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Bangladesh University of Engineering and Technology Mechanical Engineering Department

Report on Industrial Training

Course no.: ME 370

210 MW Shiddhirganj Thermal Power Station

Narayanganj, Bangladesh

Training Participants: Md. Jubayer Hossain(0510077)

Shuvra Banik(0510094)

Aminul Islam Khan(0510117)

Sudarshan Chandra Saha(0510119)

Md. Shoeb Hasan(0510130)

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Contents:

Topics Page number

Acknowledgement 4

1. Introduction 5

2. Plant at a glance

2.1 Machinery and equipment

6-7

3. Organogram 8

4. Simplified line diagram of 210MW STPS

4.1 Steam power plant energy conversion

4.2 Working cycle (Rankine cycle)

9-11

5. Description of boiler

5.1 Classification of boiler

5.2 Specification of the boiler

5.3 Circulation

5.4 Boiler mountings

5.5 Boiler accessories

5.6 Water wall

5.7 Cyclone separator

12-18

6. Description of Turbine :

6.1 Types of turbine

6.2 Specification of turbine

6.3 Number and location of bearing in turbine

6.4 Steam sealing in turbine

6.5 Steam regulating valve

6.6 Turning gear

18-22

3

7. Generator

7.1 Parts of generator

7.2 Working principle

7.3 Generator specification

7.4 Cooling system of generator

7.5Maintenance sequence in generator

23-26

8. Unit protection system

8.1 Electrical protection system

27

9. Start-up and shut-down of 210MW unit

9.1 Starting sequence of 210MW STPS:

9.2 Shut down

28-29

10. Description of Condenser 29

11. Description of deaerator 30

12. Description of pumps 31-34

13. Description of HPH/LPH and different heat exchanger 35

14. Water treatment system of 210MW STPS

14.1 Importance of boiler feedwater treatment:

14.2 Results of Poor Water Treatment

14.3 Water treatment process

35-44

15. Power plant performance

15.1 Efficiency

15.2 Heat rate:

15.3 Some other common performance factors

45-48

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Acknowledgement

Industrial training ME-370 is a part of our B.Sc. Engineering Curriculum. This course is

dedicated to achieve firsthand knowledge on the application of Mechanical Engineering. We are

very grateful to Mechanical Engineering Department of BUET for creating scope of training at

Shiddhirganj 210 MW Thermal Power Station(STPS), Narayanganj, Bangladesh.

We are very grateful to Shiddhirganj 210 MW Thermal Power Station for giving us the

opportunity of Industrial Training in the power plant. We attended a four weeks training at

STPS. During the training period we received full support & co-operation from the management

of STPS. We are very grateful to Md. Abdul Mannan, XEN(Shift) of STPS for his contribution

in providing training to us. Finally we would like to thank all the members of STPS especially to

Md. Fazlul Karim Chy. and Md. Jahangir Alam for their kind cooperation.

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1. Introduction:

Both the historical and the present civilization of mankind are closely interwoven with energy,

and there is little reason to doubt but that in the future our existence will ever more dependent

upon this thing called energy. Electricity is the only form of energy which is easy to produce,

easy to transport, easy to use and easy to control. So, it is mostly the terminal form of energy for

transmission and distribution. Electricity consumption per capita is the index of living standard

of people of a country.

Electricity in bulk quantities is produced in power plants, which can be of the following types:

(a) thermal, (b) nuclear, (c) hydraulic, (d) gas turbine and (e) geothermal etc. Thermal, nuclear

and geothermal power plants work with steam as working fluid and have many similarities in

their cycle and structure. Gas turbine plants are often used as peaking units. They are, however,

being increasingly used in conjunction with a bottoming steam plant in the mode of combined

cycle power generation. Hydraulic power plants are essentially multipurpose.

In Siddhirganj we had studied about 210MW thermal power station (STPS). A steam power

plant continuously converts the energy stored in fossil fuels (coal, oil, natural gas etc) into shaft

torque and ultimately into electricity. The working fluid is water which is sometimes in the liquid

phase and sometimes in vapor phase during its cycle of operations. Energy released by the

burning of fuel is transferred to water in the boiler to generate steam at a high pressure and

temperature, which than expands in the turbine to a low pressure to produce shaft work. The

steam leaving the turbine is condensed into water in the condenser where cooling water from a

river circulates carrying away the heat realized during condensation. The water is then feed back

to the boiler by the pump and the cycle goes on repeating itself.

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2. Plant at a glance:

SIDDHIRGANJ 210 MW POWER STATION

BANGLADESH POWER DEVELOPMENT BOARD

The Siddhirganj Thermal Power Plant is located on the West bank of the Shitalakhya River,

approximately 12 kilometers southeast of Dhaka City on the Narayanganj - Demra road. The

total rated capacity of the steam plant is 210 MW Commissioned on 3rd

September, 2004 by M/S

TECHNOPROMEXPORT, RUSSIA.

Capacity : 210 MW

Area of the power plant : 88.56 acre

Date of Commissioning : 03.09.2004

Total running hours of the plant : 35,103 Hrs (As on 30 September, 2009)

Energy produced since installation : 4945 MKWH (As on 30 September, 2009)

Fuel consumption per KWh : 0.27 m3

Fuel ( Natural Gas ) Cost Per unit : 0.72 Tk.

Per Unit Cost : 1.69 Tk

Plant Thermal Efficiency : 36%

2.1 MACHINERY AND EQUIPMENT :

1.Boiler:

A. Manufacturer …………………………………………….……………….TKZ, RUSSIA.

B. Boiler capacity (Superheated steam).......................................................................670 t/h.

C. Reheat Steam flow rate …………...........................................................................580 t/h

D. Superheated steam to temperature............................................................................545 0C

E. Superheated steam pressure at outlet of boiler.............................................. 138 kgf/ cm2

F. Reheat Steam temperature at Boiler inlet ................................................................334 0C

G. Reheat Steam temperature at Boiler outlet...............................................................545 0C

H. Reheat Steam pressure at Boiler inlet ......................................................... 28.4 kgf/ cm2

I. Reheat Steam pressure at Boiler outlet ........................................................ 25.9 kgf/ cm2

J. Boiler efficiency..........................................................................................................93 %

K. Feed water temperature.............................................................................................247 0C

2.Turbine:

Manufacturer …………………………………....………………………..LMZ, RUSSIA.

Nominal capacity of the turbine............................................................................210 MW

Number of Cylinder…………………………………………………………………….03

Total Number of Stage………………………………………………………………….29

Number of Extraction……………………………………………………………………7

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Frequency of the rotor rotation...........................................................................3000 r.p.m

Pressure of live steam before H.P Cylinder stop valves ………………........130 kgf/ cm2

Live steam temperature in front of the stop valves of H.P Cylinder…………….....5400C

Steam consumption on the turbine at full load.....................................................638.1 t/h

Steam consumption on the condenser at full load...................................................446 t/h

Design Pressure in the condenser.......................................0.10 kgf/ cm2

(-0.90 kgf/ cm2 )

Cooling water passing through condenser......................................................27,500 m3/h

Designed cooling water temperature at the inlet to the condenser…………...…..…240C

3.Generator:

Manufacturer …………………….………..………ELEKTROTJAZMASH, UKRAINE

Power Output........................................................................................................210 MW

Power factor.................................................................................................................0.85

Stator voltage….........................................................................................15.75 ± 5% KV

Excitation Voltage………………………………………….…………….….……...430V

Phase…………………………………………………………..………….……………..3

Stator current...........................................................................................................9060 A

Rotor current. ..........................................................................................................1950 A

Frequency. ................................................................................................................50 Hz

Stator Cooling Media…………………………………………..………………..Distillate

Rotor Cooling media...........................................................................................Hydrogen

Hydrogen pressure...............................................................................................3 kgf/cm2

Hydrogen purity..........................................................................................................97 %

Rotor Mass……………………………………………..………………..……........48 ton

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3. Organogram:

Total manpower:

Officer : 91

Staff : 348

CHIEF ENGINEER

Deputy Director (Admin.) Assistant Chief Engineer

Manager Operation Manager Maintenance

Deputy Director (Acc.)

Executive

Engineer

(Operation)

Executive

Engineer

(Shift)

Executive

Engineer

(Efficiency)

Deputy

Manager

(Operation

)

Deputy Manager

Maintenance

Executive

Engineer

Generator Executive

Engineer

Boiler

Executive

Engineer

Measuring Executive

Engineer

Turbine Executive

Engineer

Civil Executive

Engineer

Auto-control Executive

Engineer

Workshop Executive

Engineer

Electrical

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4. Simplified line diagram of 210MW STPS:

Fig: Simplified flow diagram

4.1 Steam power plant energy conversion:

Fig: Energy conversion

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4.2 Working cycle (Rankine cycle):

Generally a steam power plant works on Rankine vapor power cycle. The ideal Rankine cycle is

as follows:

Fig: Basic Rankine cycle with T-s diagram

Process 1-2: Isentropic compression in pump

Process 2-3: Constant pressure heat addition in Boiler

Process 3-4: Isentropic expansion in turbine

Process 4-1: Constant pressure heat rejection in condenser

But in practical case ideal Rankine cycle has some problems. Without superheat some water

droplets may enter into turbine and cause serious damage. Besides reheat and superheat increase

the cycle efficiency. So in 210MW STPS Rankine cycle is used with reheat and superheat.

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Fig: Rankine cycle with reheat and superheat

Fig: T-s diagram of Rankine cycle with reheat and superheat

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5. Description of boiler:

A steam boiler generates steam at the desired rate at the desired pressure and temperature by

burning fuel in its furnace. A steam boiler is a complex integration of furnace, superheater,

reheater, evaporator, economizer and air preheater along with various auxiliaries. The evaporator

is that part of steam boiler where phase change occurs from liquid to vapor, essentially at

constant pressure and temperature.

5.1 Classification of boiler:

(1) According to the contents in the tube:

Water tube boiler

Fire tube boiler

(2) According to the axis of the shell:

Vertical boiler

Horizontal boiler

(3) According to the method of circulation of water and steam:

Natural circulation boiler

Forced circulation boiler

(4) According to the use:

Stationary boiler

Mobile boiler

(5) According to the source of heat:

Solid fuel boiler

Liquid fuel boiler

Gaseous fuel boiler

In 210 MW STPS, the boiler was water tube, horizontal axis, natural circulated, stationary and

gaseous fuel one.

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5.2 Specification of the boiler:

Manufacturer: TKZ, Russia.

Type: Ep 670-138-545G

Model: TGME-206/VSO

Rated Steam Capacity: 670 ton/hr

Reheat Steam flow rate: 580 ton/hr

Superheated Steam Temperature: 545oc

Pressure of Superheated Steam: 138 kgf/cm2

Fuel: Natural Gas

Reheated Steam temperature at boiler inlet: 334oc

Reheated Steam temperature at boiler outlet: 545oc

Reheated steam pressure at boiler inlet: 28.4 kgf/cm2

Reheated steam pressure at boiler outlet: 25.9 kgf/cm2

Boiler efficiency: 93 %

Temperature of Feed Water: 246oc

Number of burners: 12

5.3 Circulation:

The flow of water and steam within the boiler circuit is called circulation. Adequate circulation

must be provided to carry away the heat from the furnace. If circulation is caused by density

difference, the boiler is said to have natural circulation. If it is caused by a pump, it has forced or

controlled circulation. In 210 MW STPS boiler was natural circulated one.

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A simple downcomer- riser circuit connecting a drum and a header is shown in the following

figure.

Fig: Circulation

The downcomer, which is insulated, is outside the furnace, and the riser is inside it. Nearly

saturated water falls by gravity from the drum through the downcomer into the bottom header.

From the header water flows up along the riser where it partially boils with the formation of

bubbles and then back into the steam drum. The density of steam-water mixture in the riser is

less than that of saturated water in the downcomer, and as a result of this density difference a

circulation current is setup within the downcomer-riser circuit. The feedwater from the

economizer enters the drum and saturated steam is taken out of the drum to the superheater.

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5.4 Boiler mountings:

These are the fittings, which are mounted on the boiler for its proper and safe functioning. There

are many types of boiler mountings.

Water level indicator: It is an important fitting, which indicates the water level inside

the boiler to an observer. It is a safety device, upon which the correct working of the

boiler depends.

Pressure gauge: A pressure gauge is used to measure the pressure of the steam inside the

steam boiler. It is fixed in the front of steam boiler.

Safety valve: these are the devices attached to the steam chest for preventing explosion

due to excessive internal pressure of steam.

Steam stop valve: The principal functions of a stop valve are- (1) to control the flow of

steam from the boiler to the main steam pipe. (2) to shut off the steam completely when

required.

Feed regulating valve: Its function is to regulate the supply of water, which is pumped

into the boiler, by the feed pump. It can control 5% load variation. For large load

variation, to control the feed water, fluid coupling is used.

Blow off cock: The principal functions of a blow off cock are- (1) to empty the boiler

whenever required (2) to discharge the mud, scale and sediment which are accumulated at

the bottom of the boiler.

5.5 Boiler accessories:

These are devices which are used as integral parts of a boiler, and help in running efficiently.

There are many types of boiler accessories:

Feed water pump: It supplies water to the boiler through HP heaters. It is a multistage

centrifugal pump.It consumes 3MW power. In 210MW STPS there are three feed water

pump among them two are in operation and one is in standby. Feed water pressure is 185

kgf/cm2 and temperature is 167

oc. There are three couplings in each pump. Among the

three couplings first one is fluid coupling then mechanical coupling and the last one is

fluid coupling.

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Superheater: A superheater is an important device of a steam generating unit. Its

purpose is to increase temperature of saturated steam without raising its pressure. It is

generally an integral part of a boiler and is placed in the path of hot flue gases from the

furnace. The heat given up by these flue gases is used in superheating the steam. Steam

from boiler drum goes through superheater in following sequence:

Fig: Flow diagram of steam in superheater

Economizer:

An economizer is a device used to heat feed water by utilizing the heat in the exhaust flue

gases before leaving the chimney. The economizer improves the economy of the steam boto

heat feed water by utilizing the heat in the exhaust flue gases before leaving the chimney.

The economizer improves the economy of the steam boiler. The pressure and temperature at

the entry to the economizer are 182 kgf/cm2 and 245

oc respectively.

Advantages of using economizer are-

1. fuel saving

2. increase the steam raising capacity of boiler

Ceiling and radiant

superheater

Platen

superheater

HP 1st stage

convective

superheater

HP 2nd

stage

convective superheater

LP 1st stage convective

superheater

LP 2nd

stage

convective

superheater

Intermediate pressure

turbine

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3. prevents formation of scale in boiler water tubes

Air preheater:

An air preheater is used to recover heat from the exhaust flue gases. It is installed between

the economizer and the chimney. The air required for the purpose of combustion drawn

through the air preheater where its temperature is raised. It is then passed through duct to the

furnace. In 210MW STPS it is regenerative type. It rotates about 2-3 rpm.

Fig: Regenerative air preheater

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5.6 Water wall:

In 210MW STPS boiler has water cooled furnace. The combustion space of this furnace is

shielded wholly by small diameter tubes placed side by side. Water from the boiler is made to

circulate through these tubes which connects the lower and upper header of boiler.

The provision of water walls have the following advantages:

Protect the furnace against high temperature.

Avoid the corrosion of the refractory material and insulation.

Increase evaporation capacity of boiler.

5.7 Cyclone separator:

Cyclone separator utilizes the centrifugal forces for separation of mixture of steam and water in

the boiler shell, which is entered tangentially to direct the water downward and make the steam

flow upward. Then the steam goes through the zig-zag path, called dryer, on the way out to

remove the traces of moisture.

6. Description of Turbine :

Power plant produces electricity by converting chemical energy contained in fuel into thermal

energy in steam, then by converting thermal energy into mechanical energy in a turbo-generator.

One of the critical stage in converting thermal energy into mechanical energy, which occurs in

turbine. So we can say steam turbine is a kind of equipment to change thermal energy into

mechanical energy and then electrical energy by driving the generator.

6.1 Types of turbine:

(1) According to method of working principle

Impulse turbine

Reaction turbine

(2) Based on steam pressure

Low pressure turbine (1.2 to 2 MPa)

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Intermediate pressure turbine (2.1 to 4 MPa)

High pressure turbine (8.1 to 12.5 MPa)

Super high pressure turbine (12.6 to 15.6 MPa)

(3) Based on thermal property

Condensing steam turbine

Double reheat steam turbine

Adjustable extraction steam turbine

(4) Based on number of casing

Single casing steam turbine

Double casing steam turbine

Multi-casing steam turbine

6.2 Specification of turbine:

1. Manufacturer …………………………………....…………………..LMZ, RUSSIA.

2. Nominal capacity of the turbine......................................................................210 MW

3. Number of Cylinder……………………………………………………………….03

4. Total Number of Stage…………………………………………………………….29

5. Number of Extraction………………………………………………………………7

6. Frequency of the rotor rotati......................................................................3000 r.p.m

7. Pressure of live steam before H.P Cylinder stop valves …………........130 kgf/ cm2

8. Live steam temperature in front of the stop valves of H.P Cylinder………...5400C

9. Steam consumption on the turbine at full load...............................................638.1 t/h

10. Steam consumption on the condenser at full load.............................................446 t/h

11. Design Pressure in the condenser..................................0.10 kgf/ cm2 (-0.90 kgf/ cm

2 )

12. Cooling water passing through condenser................................................27,500 m3/h

13. Designed cooling water temperature at the inlet to the condenser…………..…240C

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Fig: Turbine section in 210MW STPS

6.3 Number and location of bearing in turbine:

There are five bearings in the turbine in 210MW STPS. Of them only one is thrust bearing, rest

of the bearings are journal bearing. Thrust bearing is in second position when viewed from the

high pressure turbine side. It is in between high pressure turbine and intermediate turbine. The

gap between journal and bearing is 0.6 mm.

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In thrust bearing, there are 10 set of thrust pad and a disc type coller. Pads are of two types-

active and inactive. Pads are changeable and should be replaced after a certain period of time.

6.4 Steam sealing in turbine:

Fig : Sealing of steam in turbine

Labirinth seal is one type of seal where steam itself is used to prevent it from going out side the

turbine. There is a gap between turbine shaft and circular casing which is about 1mm or less.

6.5 Steam regulating valve:

In 210MW STPS there are four steam regulating valve. These are located at the top part of the

turbine. They are controlled by governor. They regulate the steam flow into the turbine

depending on the load.

Fig: Steam regulating valve

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6.6 Turning gear:

During shut down or when the turbine is tripped, there is no steam supply to the turbine. If the

turbine which was rotating at 3000 rpm is suddenly stopped, due to inertia of motion, the rotor

may get bent and distorted. There will also be thermal stresses developed due to non-uniform

cooling. The reverse happens when the turbine is started. The turbine requires to be heated

slowly and its rated speed is reached gradually in several steps.

The turning gear is a mechanism which keeps the turbine shaft rotating at about 3 rpm to avoid

springing the shaft because of unequal expansions and contractions when warming or cooling the

turbine. It consists of a gear integral with the turbine shaft which is driven by an electric motor

through the necessary speed reduction equipment.

Fig: Turning gear operation

During shut down or when tripped, the turbine is put on turning gear automatically and it keeps

on rotating for about two days to cool down gradually and absorb the inertia of motion.

Similarly, while starting the turbine, it is put on turning gear first to keep it in rotation at low rpm

and then steam is admitted slowly by opening the stop valve till the rated speed is reached. When

the first critical speed (approximately 2200rpm) is approached, steam is admitted quickly to

avoid this speed.

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7. Generator:

The rotational mechanical energy of the turbine is converted to electrical energy in the generator

by the rotation of the rotor’s magnetic field. The rotation of the turbine turns the rotor of the

generator, producing electrical energy in the stator of the generator. The generator rotor consists

of a steel forging with slots for conductors that are called the field windings.

7.1 Parts of generator:

Usually a generator consists the following parts:

Stator winding (conductor)

Rotor (magnet)

Stator core

7.2 Working principle:

An electrical direct current is passed through the windings, causing a magnetic field to be formed

in the rotor. This magnetic field is rotated by the turbine. The rotor is surrounded by the stator

that includes copper conductors. The magnetic field of the rotor passes through the stator, setting

the electrons in the stator conductor in motion. The flow of electrons is called current. As the

rotor’s North Pole passes through the stator conductors, the current flows in one direction.

When the south pole of the rotor’s magnetic field passes through the same direction, the current

flows in the opposite direction. This type of current is called the alternating current (AC).

7.3 Generator specification:

Manufacturer …………………….………..………ELEKTROTJAZMASH, UKRAINE

Power Output........................................................................................210 MW/ 247MVA

Power factor.................................................................................................................0.85

Stator voltage….........................................................................................15.75 ± 5% KV

Excitation Voltage………………………………………….…………….….……...430V

Phase…………………………………………………………..………….……………..3

Phase connection………………………………………………………………………..Y

Stator current...........................................................................................................9060 A

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Rotor current. ..........................................................................................................1950 A

Speed of rotation………………………………………………………………..3000 rpm

Frequency. ................................................................................................................50 Hz

Stator Cooling Media…………………………………………..………………..Distillate

Rotor Cooling media...........................................................................................Hydrogen

Hydrogen pressure...............................................................................................3 kgf/cm2

Hydrogen purity..........................................................................................................97 %

Rotor Mass……………………………………………..………………..……........48 ton

Efficiency ………………………………………………………………………..98.45%

Static over load……………………………………………………………………....1.71

Short circuit ratio…………………………………………………………………….0.52

There with:

- Altitude above sea level up to 1000m.

- Lower value of ambient air temperature limit up to +5oc.

- Hydrogen characteristics:

Hydrogen rated gauge pressure 0.3MPa

Hydrogen purity in percent of volume > 97%.

- Characteristics of water entering the gas cooler:

Flow rate 111.1 lit/sec.

Temperature at inlet 34oc.

Gauge pressure 0.35MPa.

Pressure drop in gas cooler 0.08 MPa.

- Characteristics of water entering the first heat exchanger circuit:

Flow rate about 56 lit/sec.

Temperature at inlet 34oc.

Gauge pressure at inlet < 0.6 MPa.

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- Characteristics of distillate, entering stator winding :

Flow rate 12 lit/sec.

Temperature at inlet 41oc.

Gauge pressure at inlet < 0.28MPa.

Gauge pressure at stator winding outlet 0.05-0.1MPa.

Distillate resistivity at 41oc > 75kΩcm.

- Oil characteristics for bearings and seals:

Flow rate through the two bearings 10 lit/sec.

Flow rate through the two seals 3.3 lit/sec continuous duty.

Short time, but not longer than 30 minutes, 5 minutes.

Gauge pressure at entering the bearing 0.1- 0.17MPa.

Oil-to-hydrogen pressure drop 0.075 ± 0.005MPa.

Temperature at entering the bearings and seals 35-45oc.

7.4 Cooling system of generator:

Due to resistance, heat generates, so cooling is necessary. For small power plant cooling is done

by air. In 210MW STPS to cool the generator hydrogen (H2) and water (H2O) are used. Large

generators are cooled with hydrogen. The thermal properties of hydrogen (like specific heat and

thermal conductivity) are superior to those of air and allow for reduced and better cooling.

Windage and ventilating losses are lower because of the low density of hydrogen. Stator

windings are distillate water cooled. Rotor and stator core are hydrogen cooled. Minimum

resistance of water 75kΩ/cm is required. Maximum pressure of water at inlet 2.8 kgf/cm2 and at

outlet 1.0 kgf/cm2 are required. Minimum hydrogen pressure 3 kgf/cm

2 is required. If hydrogen

pressure reduced to 2.9 kgf/cm2 H2 should be injected to increase the hydrogen pressure. To seal

the whole system sealing oil pressure 3.7kgf/cm2 is maintained. Hydrogen purity is maintained

99.9 %. If purity falls to 97 %, control system gives a signal. Regulating valve always maintain

0.8kgf/cm2 pressure difference between water and hydrogen.

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7.5 Maintenance sequence in generator:

Since hydrogen is explosive in contact with air, to avoid this hazard the following sequence is

followed during maintenance.

During Opening:

1. Hydrogen out

2. Carbon dioxide (CO2) in

3. When the percentage of CO2 is reached to 99-100 %, air is introduced and CO2 gets out.

4. Open the generator

Process 1 and 2 occurs simultaneously.

During closing:

1. Air out

2. CO2 in

3. When percentage of CO2 is reached to 99-100%, hydrogen is introduced and CO2 gets

out.

4. When hydrogen purity reached to 99.9%, generator is closed.

27

8. Unit protection system:

Two type of protection system are used in 210MW STPS. These are

(1) Electrical protection system

(2) Technical protection or process protection

8.1 Electrical protection system:

The following electrical protection systems are used to avoid the failure of the system-

Differential protection.

Earth fault protection.

Over load protection.

Over voltage protection.

Over frequency and under frequency protection.

Over fluxing protection.

Reverse power protection.

Low forward power protection.

Thermal protection.

Distance protection.

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9. Start-up and shut-down of 210MW unit:

9.1 Starting sequence of 210MW STPS:

The following starting sequences are followed-

1. Start circulating water pump(CWP).

Check- oil level, cooling water supply, bearing lubricating oil supply, vacuum pump

check up etc.

2. Fill the deaerator

To fill the deaerator start condensate pump.

For deaeration recirculate water between condenser and deaerator for about one hour.

3. Fill the boiler drum.

Boiler drum is filled up to a certain level by starting feed pump. Vent valve of boiler

drum is kept open to remove air. Drains valve of different steam containing pipes are also

kept open to remove condensate that form initially. Latter these valves are closed.

4. Fire the boiler

Firing is done in following sequence

a. Start ID fan

b. Start FD fan

c. Start regenerative air preheater.

Then purging is accomplished. It takes three minutes.

5. Initially steam temperature is less so some steam at pressure(15kgf/cm2) is released to

atmosphere. Latter steam vent is closed when temperature rises. A small part of the steam

is taken to auxiliary header reducing the steam pressure to abut 10kgf/cm2. From

auxiliary header steam is sent through ejector pump to remove air from condenser to

create vacuum. Start the turning gear(300oc, 25-30kgf/cm

2).

6. Check the steam condition:

If it is ok. Run the turbine at about 500rpm for half an hour.

7. Again check steam condition.

If it is ok. Run the turbine at about 1000rpm for half an hour.

8. After checking the condition again, using steam to go turbine at 3000rpm. From 1000-

2300rpm speed should be reached faster because natural vibration of turbine and

29

generator falls in this range. If speed increase in this range occurs slowly, resonance may

damage the equipments.

9. Take 5-10MW load, again check all steam parameters.

10. Then gradually increase temperature and pressure which will take higher load.

9.2 Shut down:

Before shut down load is cut down to 70 MW. Then switch off. After shutting off, turning gear

runs for about 72 hours at 3rpm.

10. Description of Condenser:

A condenser where the exhaust steam from the turbine is condensed operates at a pressure lower

than atmosphere. Condenser works below atmospheric pressure so as to increase the specific

output of the turbine which in turn increase the efficiency of the boiler.

In 210MW STPS a shell and tube type condenser is used. Cooling water passes through the tube

and steam passes outside the tube. Tubes are made by Cu based metal. There are huge number of

tubes( > 12000). The inside temperature and pressure are 45oc and 0.1kgf/cm

2(-0.9kgf/cm

2).

Ejector pump is used to vacuum the condenser. The working principle of the ejector pump is

based on venturimeter (Bernauli’s principle).

Fig: Method of creating vacuum in condenser

30

11. Description of deaerator:

Fig: Deaerator in 210MW STPS

It is used for the purpose of deaerating the feed water. The presence of dissolved gases like

oxygen and carbon dioxide makes the water corrosive, as they react with the metal to form iron

oxide. The solubility of these gases in water decreases with increase in temperature and becomes

zero at boiling or saturation temperature. These gases are removed in the deaerator, where the

feed water is heated to saturation temperature by the steam extracted from the turbine.

deaerator

31

12. Description of pumps:

In 210MW STPS different types of pumps used are as follows:

12.1 Vacuum pump:

Vacuum pump is used to create vacuum to bring the syphon come into action. There are

two vacuum pumps. One runs and another remains standby. The siphon is used for

following purposes-

For maintenance of the pump: it keeps the water reservoir separate from river. So

water can be removed from the reservoir and maintenance can be performed.

It also maintains a constant level of water in the reservoir tank. So change of

water in the reservoir tank does not occur due to change of water level in the river

at winter.

It prevents heavier objects to enter into the pump suction.

Fig: syphon

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Fig: Vacuum pump

12.2 Circulating water pump(CWP):

There are 3 circulating water pumps, two of them are running and one remains standby.

These are one of the most important pumps as and they supply water to water treatment

plant, firefighting units and they supply water to all the place where cooling is necessary

(example- condenser cooling water). The model of the circulating pump is 96Π-4,5/2,3

TB3.

Specifications of CWP are given below-

They are vertical pump with rigidly fixed blades.

Discharge rate=4,5 m3/h.

Head of the pump is 2,3 m of water.

Capacity of pump is 1040kw.

Weight of the pump is 6240 kg.

Efficiency of the pump is 88%.

They rotate at a speed of 485rpm.

They are provided with thrust bearing.

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Fig: motor & impeller shaft of CWP Fig: river water collection by syphon

Fig: Syphonic action and water supply to CW pump

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12.3 Drip/Drain pump:

Some steam condense in the heater(LPH,HPH). A portion of the water is sent to feed line

and a portion to the condenser using drip pump.

12.4 Technical water pump:

It is used for cooling the bearings of pumps and fans.

12.5 Gas cooling pump:

It supplies river water to cool the coolant hydrogen used in generator.

12.6 Raw water pump:

It pumps the water from CWP output to water treatment plant.

12.7 Oil pump:

Main oil pump:

Located in the casing of governor. It comes into action when turbine

reaches a certain speed after start.

Starting oil pump:

It supplies oil during start up of the steam turbine generator.

Standby oil pump:

It comes into action when oil pressure goes to 0.7 kgf/cm2 or less.

12.8 Emergency oil pump:

It is run by DC supply. It starts when pressure falls below 0.3kgf/cm2.

12.9 Sealing oil pump:

It supplies oil to seal Hydrogen in generator.

12.10 condensate water pump:

Model: kcB-320-160-2T3϶

Capacity: 320m3/hr.

Head: 160m

Number of version: 2

Number of stage: 3

Alignment: vertical.

It supplies condensate water to feed water tank through LP heaters at a temperature and

pressure 47oc and 16kgf/cm

2 respectively.

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13. Description of HPH/LPH and different heat exchanger:

Feed water heaters are always used in steam power plant to improve the cycle efficiency. They

raise the temperature of feed water before it enters the economizers. Both open and close type

are used. In 210 MW STPS there are seven feed water heaters. All of them are closed type

heater. Among them four are called low pressure(LP) heater and rest three are called high

pressure(HP) heater based on operating pressure. LP heater works at around 13.6-16kgf/cm2

pressure. HP heater works at a pressure of around 182-185kgf/cm2.

Seven extraction lines are made to heat the water passing through the feed water heater. Three

extractions are made from the high pressure turbine and four extraction lines are made from

intermediate and low pressure turbine.

14. Water treatment system of 210MW STPS:

14.1 Importance of boiler feedwater treatment:

Maintaining good feedwater is an important and fundamental aspect of any steam turbine power

plant. A plant that maintains good

feedwater achieves the following three benefits:

1. Help to ensure maximum life out of its boilers, steam turbines, condensers, and pumps.

2. Reduce maintenance expenses.

3. Maintain optimal thermal performance

14.2 Results of Poor Water Treatment:

In the ideal situation, water would be feed to a boiler free of any impurities. Unfortunately, this is

not the case. Water clean up is always required. The following items are the most problematic to

boilers and steam turbines:

Calcium (Ca) scale– Calcium forms with sulfates (SO4 ) and other compounds to form calcium

sulfate, calcium bicarbonate, calcium carbonate, calcium chloride, and calcium nitrate. During

36

evaporation, these chemicals adhere to boiler tube walls forming scale. Its formation increases

with the rate of evaporation so these deposits will be heaviest where the gas temperatures are

highest. Scale is a nonconductor of heat which leads to a decreased heat transfer of the boiler

tubes, and can result in tube failure due to higher tube metal temperatures. Buildup of scale also

clogs piping systems and can cause control valves and safety valves to stick.

Magnesium (Mg) scale – Same issues as with calcium.

Silica (SiO2) – Silica can form scale at pressures below 600 psig. Above 600 psig, silica starts to

volatize, passing over with steam to potentially form deposits on the steam turbine diaphragms

and blades. These deposits change the steam path components’ profiles resulting in energy

losses. The degree of loss depends upon the amount of the deposits, their thickness and their

degree of roughness.

For example, if the nozzle area of the first stage flow path was reduced by 10%, the output of the

steam turbine would be approximately 3% less. A similar loss could occur if the gas turbine

received steam for power augmentation purposes.

Sodium (Na) – Sodium can combine with hydroxide ions creating sodium hydroxide (caustic).

Highly stressed areas of boiler piping and steam turbines can be attacked by sodium hydroxide

and cause stress-corrosion cracks to occur. This was a problem in older boiler with riveted drums

because of stresses and crevices in the areas of rivets and seams. While less prevalent today,

rolled tube ends are still vulnerable areas of attack as well as welded connections.

Chloride (Cl) – Chlorides of calcium, magnesium, and sodium, and other metals are normally

found in natural water supplies. All of these chlorides are very soluble in water and therefore,

can carry over with steam to the steam turbine. Chlorides are frequently found in turbine deposits

and will cause corrosion of austenitic (300 series) stainless steel and pitting of 12 Cr steel.

Corrosion resistant materials protect themselves by forming a protective oxide layer on their

surface. These oxides are better known by their generic name “ceramic.” All ceramics will pit if

exposed to chlorides. If the metal piece is under tensile stress either because of operation or

residual stress left during manufacturing, the pits formed by chlorides attacking the passive layer

37

will deepen even more. Since the piece is under tensile stress, cracking will occur in the stressed

portions. Usually there will be more than one crack present causing the pattern to resemble a

spider’s web. The most common source of chloride contamination is from condenser leakage.

Iron (Fe) – High iron is not found in raw water but high concentrations can come from rusted

piping and exfoliation of boiler tubes. Iron is found in condensate return in a particle form as it

does not dissolve in water. The detrimental aspect of iron is called steam turbine solid particle

erosion, which causes significant erosion of steam turbine steam path components.

Oil – Oil is an excellent heat insulator, and adherence of oil on tube surfaces exposed to high

temperatures can cause overheating and tube damage.

Oxygen (O2) – Oxygen is found in feedwater and its partial pressure is relatively high so it will

requires a near saturation temperature to disassociate itself from water. Oxygen in combination

with water will attack iron and cause corrosion. The reaction occurs in two steps:

Fe++ + 2OH- = Fe(OH)2

Ferrous ion Hydroxyl ion Ferrous hydroxide

Then

4Fe(OH)2 + O2 + 2H2O = 4Fe(OH)3

Soluble Dissolved Water Insoluble

Ferrous oxygen ferric

Hydroxide hydroxide

The ferric hydroxide is highly insoluble and precipitates on heated surfaces. The precipitate is

called magnetite or rust. The closer the water is to the saturation temperature, the more corrosion

will occur.

38

Carbon Dioxide (CO2) – Carbon dioxide can react with water to form carbonic acid (H2CO3).

Carbonic acid will cause corrosion in team and return lines. Carbon dioxide can originate from

condenser air leakage or bicarbonate (HCO3) alkalinity in the feedwater.

pH – The pH value of water is a measure of its alkalinity or acidity and has a direct bearing on

the corrosive properties. All water contains alkaline (hydroxyl, OH) ions and hydrogen (H) ions.

The product of the concentrations is always approximately 10-14. The pH value of the water is

the log of the reciprocal of the H ion value. If the water is neutral, the OH and H ion

concentrations are each 10-7. A pH below 7 indicates acidity; over 7 designate an alkaline

condition. Low pH in local areas is the second most common cause of corrosion in mild steel

boilers above roughly 400°c, mild steel corrosion results in the formation of magnetite, a tight

adherent that acts as a barrier between boiler water and steel. The corrosion reaction stops after a

uniform magnetite layer is formed.

Rapid general corrosion can ensue if this protective film is disrupted, so water chemistry must be

carefully controlled to maintain the film. An acidic condition can destroy the magnetite film;

therefore, boiler water is maintained in the alkaline range of a pH of 9.0 to 10.5.

Foaming – Foaming is the formation of bubbles or froth on the water surface. It is caused by a

high amount of total and suspended solids. Foam will fill the free surface area of a separating

device increasing local velocities and promoting a serious carryover of boiler water.

Priming – Priming is a violent and spasmodic discharge of water with steam into the steam

space. Slugs of water are thrown over with the steam causing damage to the steam turbine.

Carryover – When boiler water solids are carried over into the moisture mixed with steam even

though there is no indication of foaming or priming, this is considered as carryover. Carryover

can be the result of high steam flow which overloads the dryers (separators). The dryers work by

sudden changes in stem velocity so that foreign particles are thrown out by centrifugal force.

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14.3 Water treatment process:

Coagulation method

Coagulation is intended for water cleaning from fine & coarse suspension,

colloidal structure & also discoloring. It is also carried out by special reagent or coagulants

(Al2(SO4)3.18H2O ) .

Al2(SO4)3 + 3Ca(HCO3)2 Al(OH)3 + 3CaSO4 + 6CO2

Gas out

Fig: Clarifier

Conditions:

Transparency: 30 cm of ring observation.

Alkinity: 0.4-0.6 mge/L

pH value: 6.1-6.6

Pump

Collector

Grit

Heavy particles

goes down

Natural

water

Clean

water

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Mechanical Filter

It is the process of clarification that takes place as a result of adhesion of

suspended particles to anthracite grains.

Grain size: 0.8-1.8 mm

Fig: Mechanical filter

Anthracite grain

Water in Clean water

Out

41

Fig: Dosing pump

Cat-ion exchanger:

Cat-ion method of water softening is based on it’s capability of some practically

insoluble material in water to enter into ion exchange process to dissolved salts absorbing from

the water their cat-ions.

2HR + CaSO4 = CaR2 + H2SO4

HR + CaCl2 = CaR2 + 2HCl

HR + MgSO4 = MgR2 + H2SO4

HR + Ca(HCO3)2 = CaR2 + H2O + CO2

Resin Acidic Water

Regeneration of Cat-ion:

After a while the quantity of HR goes down. So regeneration required.

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CaR2 + H2SO4 = CaSO4 + HR

CaR2 + HCl = CaCl2 + HR

4-6% HCl or H2SO4 is used for regeneration.

Fig: Ion exchanger

Decarbonizer:

Decarbonization unit is intended for the removal of dissolved carbonic acid which

appears as a result of H2 decarbonization of H2O.

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Fig: Decarbonizer

Anion exchanger:

Anion filter is designed for removal o f all strong basic anion available in

cat-ionated (Acidic water) water.

ROH + H2SO4 = R2SO4 + H2O

ROH + HCl = R-Cl + H2O

Regeneration of anion:

R2SO4 + 2NaOH = ROH + Na2SO4

R-Cl + NaOH = R-Cl + NaCl

4-6% NaOH is used for this purpose.

CO2

Fan

Water in

Grit

Storage of CO2

free water

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Mixed bed filter:

The purpose of MBF is the filtration of water after anion filter for deep

absorption of impurities like Na+, SiO2

-, Cl

-. It is a combination of cation exchanger & anion

exchanger.

Fig: Mixed bed filter

De-mineralised water quality:

Conductivity = Max 0.3 µs/cm

Silica, SiO2= 0.02 mg/L

Water in

Water out

Cat-ion exchanger

Anion exchanger

45

15. Power plant performance:

In an ideal situation, all of the chemical energy in the fuel would be converted in to electrical

energy. However, this does not happen, because a great deal of energy is lost in the plant cycle.

The result is that the amount of electrical energy that comes out of the plant is much less than the

amount of chemical energy that goes into the plant from natural gas. Practically, it is impossible

to avoid the losses occur in the pant cycle. Therefore, plant performance is carefully measured so

that inefficiencies in the plant cycle can be spotted and corrected as quickly as possible. Plant

performance is usually measured in two ways-

(1) efficiency

(2) heat rate.

15.1 Efficiency:

The overall efficiency of the plant is a measure of the amount of energy that goes into the plant

compared with the amount of energy that goes out of the plant. It is usually expressed as

percentage.

Efficiency=

× 100%

The operating efficiency of 210MW STPS is 36%. That means, 64% of the chemical energy put

into the plant does not go out of the plant as electrical energy.

Calculation with real data of this plant for a particular month:

Total generation=28989450kw-hr (from energy meter)

Total fuel consumption=9065463m3(in STP) [From fuel consumption meter]

Maximum load in the month=120MW

Plant rated capacity=210MW

We know, 1kw-hr= 860 cal

Fuel heating value=8372.73 kcal/m3

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So thermal energy=

=

=32.84%

15.2 Heat rate:

Heat rate is a measure of the relationship between the energy that is put into a plant and the

energy that goes out of the plant. However, unlike efficiency, which is expressed as a percentage,

heat rate is a direct measure of the amount of chemical energy required to produce each kw-hr of

electricity.

Heat rate=

(kcal/kw-hr)

Heat rate=

Heat rate=

The value of heat rate is around 2600kcal/kw-hr. In other words, 2600 kcal of chemical energy

are typically required to produce one kw-hr of electricity.

Calculation with real data of this plant for a particular month:

Heat rate=

=

=2618.29kcal/kw-hr

Major factors affecting heat rate:

1. The temperature of superheated steam entering the turbine

2. The vacuum in the condenser

3. The temperature of feed water

A turbine is designed to operated most efficiently when it is supplied with steam at a specific

temperature. When steam temperature varies from the turbine’s design operating temperature,

47

both the turbine efficiency and plant heat rate are affected. Generally, a decrease in superheated

steam temperature causes an increase in heat rate. If the heat rate becomes greater than the

design heat rate, then the plant operates less efficiently. An increase in superheated steam

temperature causes a decrease in heat rate. A decrease in heat rate means that the plant is

operating more efficiently. It should be noted, however, there is a limit to how much temperature

plant system are designed to handle. If the superheated steam temperature increases too much, it

may cause serious damage to plant components.

When condenser vacuum decreases, the turbine operates less efficiently, because less energy is

removed from the steam passing through the turbine. As a result, less electrical energy is

produced; the plant’s heat rate increases, and its efficiency decreases.

Feedwater heaters increase the temperature of feed water before it enters the boiler. If feed water

temperature is close to boiling, then less energy is required to turn the water back into steam.

Feed water heaters use extraction steam from the turbine to heat feed water. Most of the energy

in the extraction steam would otherwise be lost to the system. Therefore, plant efficiency is

increased by heating feed water and by using energy in the extraction steam. In general, the

higher the feed water temperature, the lower the heat rate and the greater the efficiency of the

plant.

15.3 Some other common performance factors:

Load factor:

Load factor of a power plant is the ratio between average load and maximum load for a period

and can be expressed as follows:

Load-factor=

32.47%

Plant factor/capacity factor:

Plant factor of a plant is the ratio between the average load and rated load of that plant for a

period and can be expressed as :

48

Plant-factor=

Availability factor:

The ratio between the running hours of the plant and the total hours for that particular period and

can be expressed as :

Availability factor=

Fuel consumption per unit:

The ratio between fuel consumption and total generation for that particular period and can be

expressed as:

Fuel-consumption-per-unit=

Nm3/kw-hr